+C2TRuoXurRuF000To discrete components amplifiers, theinputquantitycan be Ubeor ibMicroelectronicCircuits
Microelectronic Circuits To discrete components amplifiers，the input quantity can be Ube or ib
The judgment of DC feedback and ACfeedback0550u,AAA000uououoR2R2R2(b)(a)(c)oWDCfeedback,noACfeedbackAOuoR2CACfeedback,noDCfeedbackMicroelectronic Circuits
Microelectronic Circuits AC feedback，no DC feedback DC feedback，no AC feedback The judgment of DC feedback and AC feedback
Example:feedback? Positiveornegative? DC or AC?R3+o+RuAluR,uolXARuo+U1R4AC and DC negativefeedbackMicroelectronic Circuits
Microelectronic Circuits Example ：feedback？Positive or negative？DC or AC？ AC and DC negative feedback
The General Feedback EguationSourceLoad=Ax+>Open loopgainA>FeedbackfactorβXf = βx。>Loop gainAβA>ClosedloopgainAfx.>Amount of feedback (1+ Aβ)1+ Aβx.SMicroelectronic Circuits
Microelectronic Circuits The General Feedback Equation f o o i x x x Ax = = A A x x A s o f + = 1 ➢Open loop gain A ➢Feedback factor β ➢Loop gain Aβ ➢Closed loop gain Af ➢Amount of feedback (1+ Aβ)
The General FeedbackEguationSourceLoadA,~/β>If Aβ >>1, The gain of the feedbackamplifierisalmostentirelydeterminedbythefeedback network.AβXXf>If Aβ >>1, which implies that the signal Xi1+ Aβat the input of the basic amplifier is reducedto almost zero.X=xMicroelectronic Circuits
Microelectronic Circuits The General Feedback Equation 1 Af f s f s x x x A A x + = 1 ➢If Aβ >>1, The gain of the feedback amplifier is almost entirely determined by the feedback network. ➢If Aβ >>1, which implies that the signal Xi at the input of the basic amplifier is reduced to almost zero